Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $93.46   5.107%   $98.233   $98.23   $98.25   $98.20  
  Purchase #2 $66.71   4.469%   $69.6913   $69.69   $69.70   $69.70  
  Purchase #3 $25.91   12.517%   $29.1532   $29.15   $29.15   $29.20  
  Purchase #4 $212.44   10.216%   $234.1429   $234.14   $234.15   $234.10  
  Purchase #5 $20.53   6.555%   $21.8757   $21.88   $21.90   $21.90  
  Purchase #6 $165.47   10.721%   $183.21   $183.21   $183.20   $183.20  
  Purchase #7 $243.54   8.581%   $264.4382   $264.44   $264.45   $264.40  
  7 purchase totals = $828.06       $900.7443   $900.74   $900.80   $900.70